We used this apparatus to measure components of flux. There was an alternating current in the copper Helmholtz coil which created an alternating flux inside the circle. The thing propped on the pink ruler in the middle is a search coil. The changing flux passes through this coil and induces an emf which is measured by an oscilloscope. We plotted the angle of between the search coil and the Helmholtz coil versus the peak voltage. You get a rough straight line if you plot the sine of the angle.
